Twenty arrests were made by police as a splinter group left an organised rally against public spending cuts and marched to a city centre.

Up to 4,000 protesters had gathered peacefully in Manchester on Saturday to hear claims from union leaders that the Government was "betraying" young people, but trouble erupted when several hundred later broke through police lines.

Those arrested - all men - were detained on suspicion of various public order offences.

Two officers suffered minor injuries, one was bitten.

Police said the breakaway group was intent on inciting violence and causing damage as intelligence suggested a number were armed with chefs' knives and one man arrested possessed razor blades.

They said the rally organisers - the TUC, NUS (National Union of Students) and UCU (University and College Union) - had dissociated themselves from the city centre unrest and said they were nothing to do with the organised demonstrators.

A Greater Manchester Police spokesman said: "The final number of arrests following yesterday's demonstrations is 20.

"Thirteen were arrested for section five public order offences, six for breach of the peace and one for obstructing a public highway."

No further details of the police operation would be released, he added.

The protest, aimed at highlighting the effects of Government spending cuts on young people, started in acrimony when NUS president Aaron Porter withdrew as a speaker when he was surrounded by angry demonstrators who called for him to quit his post.